A TFT-LCD has the advantages of portability, low power consumption, and low radiation, and has been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras and the like. Furthermore, the TFT-LCD is considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions.
FIG. 6 is an abbreviated circuit diagram of a typical TFT-LCD. The TFT-LCD 10 includes an LCD panel (not shown), a data driving circuit 2, and a gate driving circuit 1. The LCD panel includes a thin film transistor (TFT) substrate (not shown), a color filter (CF) substrate (not shown) arranged in a position facing the TFT substrate, and a liquid crystal layer (not shown) sandwiched between the TFT substrate and the CF substrate.
The TFT substrate includes a number n (where n is a natural number) of gate lines (G1-Gn) that are parallel to each other and that each extend along a first direction, and a number m (where m is also a natural number) of data lines (D1-Dm) that are parallel to each other and that each extend along a second direction orthogonal to the first direction. The TFT substrate also includes a plurality of thin film transistors (TFTs) 3 that function as switching elements. The TFT substrate further includes a plurality of pixel electrodes 6 formed on a surface thereof facing the CF substrate. Each TFT 3 is provided in the vicinity of a respective point of intersection of the gate lines (G1-Gn) and the data lines (D1-Dm).
The CF substrate includes a plurality of common electrodes 7 opposite to the pixel electrodes 6. In particular, the common electrodes 7 are formed on a surface of the CF substrate facing the TFT substrate, and are made from a transparent material such as ITO (Indium-Tin Oxide) or the like.
Each TFT 3 includes a gate electrode 31, a source electrode 32, and a drain electrode 33. An exemplary one of the TFTs 3 is labeled in detail in FIG. 6. In this TFT 3, the gate electrode 31, the source electrode 32, and the drain electrode 33 are connected to a gate line Gn-1, a data line Dm-1, and one pixel electrode 6 respectively. The pixel electrode 6, the common electrode 7 and the liquid crystal material sandwiched between the pixel electrode 6 and one common electrode 7 are represented as a liquid crystal capacitor (Clc) 8. A storage capacitor (Cs) 4 is formed between a next gate line Gn and the drain electrode 33 of the TFT 3.
FIG. 7 shows abbreviated voltage waves of a plurality of scanning signals generated by the gate driving circuit 1. V5 represents a gate-on voltage that is a high voltage generated by the gate driving circuit 1. V6 represents a gate-off voltage that is a low voltage generated by the gate driving circuit 1. The gate driving circuit 1 sequentially provides a gate-on voltage and a gate-off voltage as a scanning signal to one gate line Gn each time. In a frame time (shown as a double-headed arrow), the gate driving circuit 1 sequentially scans the gate lines from G1 to Gn with the scanning signals.
When the gate-on voltage V5 is provided to the gate electrode 31 of the TFT 3 via the gate line Gn-1, the TFT 3 connected to the gate line Gn-1 is turned on. At the same time, a gradation voltage Vd generated by the data driving circuit 2 is provided to the pixel electrode 6 via the data line Dm-1 and the activated TFT 3 in series. The potentials of all the common electrodes 7 are set at a uniform potential Vcom. Thus, an electric field is generated due to the voltage difference between the pixel electrode 6 and the common electrode 7. The electric field is used to control the amount of light transmission of the corresponding pixel unit.
When the gate-off voltage V6 is provided to the gate electrode 31 of the TFT 3 via the gate line Gn-1, the TFT 3 is turned off. The gradation voltage that is applied to the liquid crystal capacitor 8 when the TFT 3 is turned on is maintained after the TFT 3 is turned off. The gate driving circuit 1 providing gate-on and gate-off voltages to scan the gate lines (G1-Gn) is a so-called 2-level driving method.
However, due to the storage capacitor 4 between the drain electrode 33 of the TFT 3 connected to the gate line Gn-1 and the next gate line Gn adjacent to the gate line Gn-1, the gradation voltage Vd applied to the pixel electrode 6 is liable to be distorted when a voltage of the next gate line Gn changes from the gate-on voltage V5 to the gate-off voltage V6. This kind of distorted voltage is known as a feed-through voltage. The feed-through voltage is liable to decrease the potential of the pixel electrode 6. Thus the so-called flicker phenomena may appear on a display screen of the LCD panel of the TFT-LCD 10.
What is needed, therefore, is a TFT-LCD and a method for driving the TFT-LCD which can overcome the above-described deficiencies.